This application is based upon and claims priority from prior European Patent Application No. 01-830417.0, filed Jun. 21, 2001.
1. Field of the Invention
The present invention relates to integrated circuit testing and measurement, and more specifically to the testing and measurement of integrated circuits in an automated test environment.
2. Description of Related Art
Testing and measurement is an important phase in integrated circuit design and manufacturing. Albeit the specific tests and measurements to be conducted vary greatly depending on the type of integrated circuit and the function or functions it is intended to perform, it is in general necessary to check for the absence of faults and the compliance of the circuit with the desired specifications. To do this, a relatively high number of measurements in several operating conditions is conducted.
Normally this is done in an Automatic Test Environment (xe2x80x9cATExe2x80x9d), programmed to perform several measurements in different operating conditions on specified electrical quantities, which are useful to provide a characterization of the integrated circuit, by means of a sampler instrumentation.
A large number of acquisitions by the sampler instrumentation is required. Generally stated, each acquisition is made up of five steps. A first step provides for setting up all the instruments involved in the measurement A second step provides for setting the test conditions for the integrated circuit to be tested. In a third step the sampler instrumentation performs the actual acquisition (i.e., it samples the specified electrical quantities so as to measure the integrated circuit response to the set test conditions). In a fourth step mathematical calculations are performed on the acquired data. In a fifth step all the instruments are reset.
Clearly, the test time rapidly increases with the number of acquisitions to be performed, that is with the number of different test condition setups. Up to now, two techniques have been followed in order to perform these kind of measurements.
A first technique, illustrated by a flowchart in FIG. 1, can be referred to as xe2x80x9cmulti-acquisitionxe2x80x9d. According to this technique, all five steps outlined above have to be repeated for each measurement to be conducted on the integrated circuit, that is for each test condition setup. Referring to FIG. 1, after all the instruments involved in the measurement have been set up (block 11, xe2x80x9cSTUP INSTRxe2x80x9d), an analog time acquisition routine (sampling routine) is started (block 12, xe2x80x9cT ACQ STRTxe2x80x9d). The integrated circuit under test is then put in a prescribed test condition setup (block 13, xe2x80x9cSET CONDxe2x80x9d). Such test condition setup is chosen from a set of test condition setups corresponding to several tests to be conducted on the integrated circuit. During the sampling routine the sampler instrumentation samples the specified integrated circuit characteristic quantities so as to acquire the response of the integrated circuit to the programmed test condition setup (block 14, xe2x80x9cMEASxe2x80x9d). Once the integrated circuit response has been acquired, the analog time acquisition routine is stopped (block 15, xe2x80x9cT ACQ STOPxe2x80x9d). Mathematical calculations are then performed on the acquired data (block 16, xe2x80x9cMTH CALCxe2x80x9d) and finally the measurement instruments are reset (block 17, xe2x80x9cRST INSTRxe2x80x9d).
The above steps are repeated until all the test condition setups have been implemented (block 18, xe2x80x9cLST?xe2x80x9d).
The advantage of the multi-acquisition technique resides in its ease of implementation and in the possibility of predicting the overall test time given a set of test condition setups. However, this technique is inherently time consuming, due to the need for repeating the five steps for each test condition setup. Considering that each chip of the integrated circuit coming out from manufacturing has to be tested, the time needed to perform the integrated circuit testing and measurement severely impacts the overall production cost, especially in large scale production.
A second technique, illustrated by the flowchart of FIG. 2, can be defined as xe2x80x9csingle acquisitionxe2x80x9d. According to this technique, the sampler instrumentation is started at the beginning of the testing and measurement program to start the acquisition. All the test condition setups are then sequentially implemented. The sampler instrumentation is stopped when all the test condition setups have been implemented. Referring to FIG. 2, after all the instruments involved in the measurement have been set up (block 21, xe2x80x9cSTUP INSTRxe2x80x9d), an analog time acquisition routine (sampling routine) is started (block 22, xe2x80x9cT ACQ STRTxe2x80x9d). The integrated circuit is then put in a prescribed test condition setup (block 23, xe2x80x9cSET CONDxe2x80x9d). Again, such test condition setup is chosen from a set of test condition setups corresponding to several tests to be conducted on the integrated circuit. The sampler instrumentation samples the characteristic quantities of the integrated circuit so as to acquire the response of the integrated circuit to the test condition setup (block 24, xe2x80x9cMEASxe2x80x9d). The operations corresponding to blocks 23 and 24 are repeated until all the test condition setups have been implemented (block 25, xe2x80x9cLST?xe2x80x9d).
Once the integrated circuit response to all the test condition setups has been acquired, the analog time acquisition routine is stopped (block 26, xe2x80x9cT ACQ STOPxe2x80x9d). Mathematical calculations are then performed on the acquired data (block 27, xe2x80x9cMTH CALCxe2x80x9d) and finally the instruments are reset (block 28, xe2x80x9cRST INSTRxe2x80x9d).
Compared to the multi-acquisition technique, the single acquisition technique has the advantage of saving time, because the starting and stopping of the sampling routine, the setting up of the instruments involved in the measurement and the mathematical calculations have to be performed only once.
However, it has been observed that this technique also has some drawbacks. The drawbacks of this technique reside in the instability in time acquisition, since the time of absence of signal on the quantities under measure (i.e., the time during the switch between different test condition setups) varies when switching between different pairs of test condition setups. For example, FIG. 3 is a diagram showing the response R (in mV) of an integrated circuit to six different test condition setups, for instance the response R on six different channels CH1-CH6 of a programmable Radio-Frequency (RF) integrated circuit having several different channels which all must be tested. The abscissa represents the number of samples S acquired by the sampler instrumentation. As shown, the time of absence of signal differs when switching between different pairs of channels. It is therefore difficult, if not impossible, to determine whether the sampled data relate to an effective integrated circuit response to a given test condition setup, or to a time interval between two different test condition setups. This problem becomes more and more significant with the increase in the number of different test conditions to be implemented.
Another negative consequence of this problem is the unpredictability of the time needed to complete the test program.
Additionally, it has been observed that the repeatability of the measurement between successive runs of the test program on the same integrated circuit is scarce. This is for example shown in FIGS. 4A and 4B which, similarly to FIG. 3, show the response R, in two successive runs of the test program, of six different channels CH1-CH6 of a programmable Radio-Frequency (RF) integrated circuit having several different channels which all must be tested.
In view of the state of the art, it is an object of the present invention to provide a method for testing integrated circuits that is not affected by the drawbacks of conventional testing and measurement techniques.
One embodiment of the present invention provides a method for testing an integrated circuit in an automatic test environment. According to the method, the automatic test environment is set up, and there is measured at least one electrical quantity representative of an integrated circuit response to a set of prescribed integrated circuit test conditions. The automatic test environment is reset, and the integrated circuit test conditions are changed in synchrony with a synchronization signal having a prescribed periodicity, so that all of the measurements are allotted a time slot of the same length.
Another embodiment of the present invention provides an automatic test equipment apparatus for testing an integrated circuit. The apparatus includes means for putting the integrated circuit in a set test condition, sampling circuitry for measuring a response of the integrated circuit to the test condition, and a synchronization generator coupled to the means. The synchronization generator supplies at least one synchronization signal having a prescribed periodicity to the means, and the means changes the set test condition in synchrony with the synchronization signal, so that all of the measurements are allotted a time slot of the same length.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only and various modifications may naturally be performed without deviating from the present invention.